Journal
MARINE AND PETROLEUM GEOLOGY
Volume 26, Issue 6, Pages 909-915Publisher
ELSEVIER SCI LTD
DOI: 10.1016/j.marpetgeo.2008.09.003
Keywords
Cenomanian-Turonian Boundary Event; Black shales; Sediment delta N-15; Organic delta C-13; Rock-Eval pyrolysis; TOC/TN ratio
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Funding
- Korea Science and Engineering Foundation
- U.S. Science Support Program of joint Oceanographic Institutes
- Petroleum Research Fund
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We have conducted elemental, isotopic, and Rock-Eval analyses of Cenomanian-Santonian sediment samples from ODP Site 1138 in the southern Indian Ocean to assess the origin and thermal maturity of organic matter in mid-Cretaceous black shales found at this high-latitude location. Total organic carbon (TOC) concentrations range between 1 and 20 wt% in black to medium-gray sediments deposited around the Cenomanian-Turonian boundary. Results of Rock-Eval pyrolysis indicate that the organic matter is algal Type It material that has experienced modest alteration. Important contributions of nitrogen-fixing bacteria to the amplified production of organic matter implied by the high TOC concentrations is recorded in delta N-15 values between -5 and 1 parts per thousand, and the existence of a near-surface intensified oxygen minimum zone that favored organic carbon preservation is implied by TOC/TN ratios between 20 and 40. In contrast to the marine nature of the organic matter in the Cenomanian-Turonian boundary section, deeper sediments at Site 1138 contain evidence of contributions land-derived organic matter that implies the former presence of forests on the Kerguelen Plateau until the earliest Cenomanian. (C) 2008 Elsevier Ltd. All rights reserved.
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